Halliday & Matthiessen (1999: 419):
The development of logic is of interest in itself in the present context as a tradition of 'semiotic design' whereby logical systems were developed out of the resources that have evolved in language. This design of logical systems was earned out to meet certain restricted purposes having to do with reasoning; but once such systems had been developed, philosophers and linguists turned them back on language and used them as systems for representing and theorising meaning. In the present century, when formal semantics was developed for underpinning logical systems, this was then taken as a model for work on the semantics of natural languages.